What will be the Din if only one of these conditions is fulfilled (the Nesek did not spread, but it is deeper than the skin, or it spread, but it is not deeper than the skin)?
Da'as Zekenim (citing Bechor Shor): He is Tahor, like R. Yonason in Bava Metzi'a 94b, who says that the prefix 'Vav' implies even one (unless it says "Yachdav"). 1
Da'as Zekenim (Ibid.): Whereas according to R. Yoshiyah, who says that 'Vav' implies both of them, [he is Tamei].The Bechor Shor actually presented this explanation in Pasuk 37; he did not however, say which opinion is Halachah..
Rashi extrapolates from "Lo Pasah" that if it spread, he is Tamei. Why is this necessary, seeing as "ve'Hinei Pasah" and "ve'Im Pasoh Yifseh", in Pesukim 35 & 36, teach that spreading is Metamei at the end the first or second week, or after the he has been declared Tahor?
